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On the Distribution of the different species of Rocks in the Er- 

 ratic Basin of the Ehone. By M. A. GuYOT. Communi- 

 cated by the Authoi'. 



We now know, and my preceding communications have, I 

 think, demonstrated, that the erratic Alpine formation is di- 

 -vided into a certain number of groups of rocks, or into erratic 

 basins, whose respective limits ai-e perfectly distinct. But 

 the question is more difficult to answer, whether, in the in- 

 tei'ior of each of these basins, we can determine a certain 

 order in the distribution of the different rocks there met with. 

 This subject, indeed, can scarcely be said to have been con- 

 sidered at all. Among the few authors who have occupied 

 themselves with the study of the erratic formation, M. J. A. 

 Deluc enumerates a multitude of facts, carefully arranged, 

 without endeavouring to deduce from them any argument for 

 or against the existence of a law of distribution. MM. de 

 Buch and Charpentier have slightly touched the question as 

 it relates to the basin of the Rhone. The former seems to 

 answer it in the affirmative, with regard to the granites of Mont 

 Blanc and the pudding-stones of Valorsine. The latter, who 

 admits a law of distribution for the erratic rocks in the interior 

 of the valley of the Rhone, appears to deny all regularity in 

 the appearance of the same species which cover the plain ; 

 but M. Studer, on the contrary, believes that he has found 

 one in the basin of the Aar, in the space which lies beyond 

 the high Alps. The facts which I have observed in all the 

 erratic basins, and especially in those of the Rhine, the Reuss, 

 and the Rhone, have led me to these results : — 



1*^, That the distribution of the species of erratic rocks in 

 the interior of each basin is suliject to a law which has the 

 same influence in the plains as in the valleys. 

 2dly, That this law is the same in all the basins. 

 But it is of the last only of the basins I have named that 

 I wish to speak at present. 



Tlie variety of rocks, differing as much in appearance as in 

 mineralogical cliai'acter, presented by the basin of the Rhone, 

 and the large scale on which the phenomenon is exhibited, ren- 



